High Rev Jerking

[JordanB08]

Hey guys n gals,

Where to start. I loooove my Ninja 250. Bought it with around 3K miles (now has around 4) on it, 2 prev owners and it runs like a champ. Had a small issue a bit back with the petcock causing a leak into my engine but that's all fixed up. The issue now is a bit less drastic, so i think.

While out on a ride on the highway if found that my ninja has issues with reving past 11K. I was in 6th and when I gave it throttle to speed up around 80ish it started to jerk back and forth. I tried it out on different gears and sure enough when getting to that 11k it jerks. I've looked around but cant find any forums that have this same issue. (or at least this exact same issue) I hope someone knows what im talking about!!

J

[choneofakind]

Will it rev freely to redline when not loaded! Ie can you pull the clutch in and rev it to the limiter?

Did the bike sit for any length of time from the PO before you bought it?

[jkv45]

How fresh is the fuel?

What does the air filter look like?

Bad/old fuel can give you that type of issue. Best thing to do would be to completely drain the tank and fill with 87 octane without ethanol (or the lowest grade available without ethanol) and add a fuel system cleaner like Chevron Techron Concentrate at 1oz per gal. You could drain the float bowls and see what the gas look like also.

Try that first. If it's still having an issue I would look at the plugs.

[jkv45]

Originally Posted by choneofakind

Will it rev freely to redline when not loaded! Ie can you pull the clutch in and rev it to the limiter?

Did the bike sit for any length of time from the PO before you bought it?

Huh? Revving to redlne without load? Hitting the limiter in neutral?

I'd never recommend that.

[choneofakind]

That's an easy way to tell if you're at least within a few sizes of the right main jet. If the PO messed with the intake/jetting or if the carbs are massively gunked, that would show it because it wouldn't rev freely. If the issue is his CDI and the bike is not even able to go above 11k, that would show it as well.

I'm not saying pin it there and hold it for 10 minutes, nor am I saying do it cold. Don't be an idiot. Just see during a ride if it will even hit the limiter for ~1 second or not. Pull clutch, rev. that simple. You don't even have to stop moving to do so.


I'm pretty sure that this is just a gunked up carb issue. But it's at least valid to make sure the CDI isn't faulty.

[choneofakind]

Originally Posted by jkv45

Try that first. If it's still having an issue I would look at the plugs.

A plug check is not valid unless you cut the ignition IMMEDIATELY at the rpm/throttle range in question and do a plug check on the spot.

if you want to check the top end at WOT using a plug check and get an accurate test, you'd have to rev it up to 11k at full throttle, hold it there, hit the kill switch and coast to a stop, and do a plug check on the side of the road. Not practical unless you're on a dyno.

[jkv45]

Originally Posted by choneofakind

That's an easy way to tell if you're at least within a few sizes of the right main jet. If the PO messed with the intake/jetting or if the carbs are massively gunked, that would show it because it wouldn't rev freely. If the issue is his CDI and the bike is not even able to go above 11k, that would show it as well.

I don't think it would.

Because there is no load, the amount of throttle opening necessary to get to that RPM is minimal. The slides would not lift completely.

Even under load it still takes time for the slides to lift all the way.

[jkv45]

Originally Posted by choneofakind

A plug check is not valid unless you cut the ignition IMMEDIATELY at the rpm/throttle range in question and do a plug check on the spot.

I'm not suggesting he needs to read the plug precisely, just check the general condition.

[DaBlue1]

Originally Posted by JordanB08

....While out on a ride on the highway if found that my ninja has issues with reving past 11K. I was in 6th and when I gave it throttle to speed up around 80ish it started to jerk back and forth. I tried it out on different gears and sure enough when getting to that 11k it jerks. I've looked around but cant find any forums that have this same issue. (or at least this exact same issue) I hope someone knows what im talking about!!

J

when was the last time you cleaned /inspected replaced the air filter? Kawasaki recommends replacement @ 2 years.

Also, what mods do you have on the bike?

[choneofakind]

jay, we're OT.

I'd recommend the OP runs some carb cleaner through the next tank of gas, checks the air filter, and opens the carbs just to know what's in them.

No sense wasting energy attempting to fix something that you don't know. Could be a simple case of dirty carbs, could be poor jetting, could be bad CDI. Likely it's just dirty carbs, but until the PO does some other snooping around, we're really just shooting with our eyes closed.

[jkv45]

Originally Posted by choneofakind

jay, we're OT.

I'd recommend the OP runs some carb cleaner through the next tank of gas, checks the air filter, and opens the carbs just to know what's in them.

No sense wasting energy attempting to fix something that you don't know. Could be a simple case of dirty carbs, could be poor jetting, could be bad CDI. Likely it's just dirty carbs, but until the PO does some other snooping around, we're really just shooting with our eyes closed.

I thought that's exactly what I recommended in post #3.

And thanks for the "not helpful" rating when I challenged your suggestion of revving to the limiter...

It's all been On Topic IMO.

[JordanB08]

Hey guys,

Thanks so much for the quick replies. To answer your questions:

About a month ago took the carb out and cleaned it good. While doing so I checked the spark plugs (looked good to me), and cleaned the air filter.

I did rev with no load and it broke past 11k no issue. The PO did say that it was sitting awhile in his garage. When took it home it had no fuel so i needed to take it home in my truck. Do you think its worth checking the fuel filter? I thought it looked good when i took out the petcock but maybe I was mistaken.

Thanks again for your guys help!!

[choneofakind]

Have you had a chance to check the airbox for blockages? Seems stupid, but lots of people have had stuff fall into their airbox, causing seemingly random performance problems.

[JordanB08]

Originally Posted by choneofakind

Have you had a chance to check the airbox for blockages? Seems stupid, but lots of people have had stuff fall into their airbox, causing seemingly random performance problems.

Checked the airbox, looks good. I also drained the tank put in new fuel, cleaned out both fuel filters (Thought 08's didnt have an inline one but they do!)

I took it out again and this time it seems worse! hahah It got me to thinking though, is the issue a fuel/air mix ratio issue? When we took out the carbs we did adjust the throttle line and choke line to have an easier time removing the carbs. Could it be possible that this issue was because of my stupidity?!?!?! Maybe its running to rich, or the opposite. Im going to look at the service manual and compare!!

J

[JordanB08]

So the issue persists heh.

I changed the oil, there was a slight smell of gas and there was more fluid indicated at the glass then when I put the oil in. Changed the filter as well. Put in some seafome with my new tank of gas. I got my hands on a carb pressure tester and one carb was a bit off; adjusted now.

I noticed when I was riding that if I pull my throttle open fast then it will hang up and jerk at 9K but if i slowly roll it on it will pass 9 and go to 11, then the problem shows its ugly face. I think it may be time to take it into a shop to get it really looked at.

Thanks again for your guys help!

J

[choneofakind]

More fluid + gassy smell = gas dripping into the oil. The two things to check for that are the petcock and the floats

[Motofool]

Originally Posted by JordanB08

..........Had a small issue a bit back with the petcock causing a leak into my engine but that's all fixed up. The issue now is a bit less drastic, so i think..........

It seems that the issue persists, being the valves controlled by the floats the main suspect.

If they don't seal properly (due to being hard or sticky), they may not open completely, restricting the flow of fuel into the bowls and leaning the mix when demand of fuel is high (high speed).

The fact that the effect is getting worse may show that the valves are getting progressively more deteriorated.

Just an hypothesis, of course.

[JordanB08]

Originally Posted by Motofool

It seems that the issue persists, being the valves controlled by the floats the main suspect.

If they don't seal properly (due to being hard or sticky), they may not open completely, restricting the flow of fuel into the bowls and leaning the mix when demand of fuel is high (high speed).

The fact that the effect is getting worse may show that the valves are getting progressively more deteriorated.

Just an hypothesis, of course.

Quite crazy that you suggest this JUST as I was inspecting the floats. I found that both needles look good except for one of the needle's springs seems weak and it wouldn't compress/decompress smoothly. What is the function of that spring on the needle! I cleaned it up and it moves smooth but as i said seems weak.

[Motofool]

Originally Posted by JordanB08

Quite crazy that you suggest this JUST as I was inspecting the floats. I found that both needles look good except for one of the needle's springs seems weak and it wouldn't compress/decompress smoothly. What is the function of that spring on the needle! I cleaned it up and it moves smooth but as i said seems weak.

The spring eliminates any vibration coming from the floats, ........... or so I believe.

A weak spring will make the level in the bowl higher than spec.
The thing is that the level of fuel in both bowls should remain as consistently as possible within the recommended range.

If the Neoprene tips look OK, check the cleanness and smoothness of the holes against which they seat and close.

http://faq.ninja250.org/wiki/How_do_..._the_floats%3F

https://www.ninjette.org/forums/show...ighlight=85429

[JordanB08]

Just wanted to come back and say thank you all for your help on this wonderful, fun, exciting journey

I found that my issue was a pinched snorkel, allowing less air then needed to get to the carb. I removed the snorkel all together and will be rejetting this afternoon when the parts get delivered. (Cant wait!!)

Thanks again!!!!!

[jkv45]

Glad you got it figured out.

Choneofakind pretty much nailed it back in post #12 when he said to check the airbox for blockages...

[csmith12]

[JordanB08]

Originally Posted by jkv45

Glad you got it figured out.

Choneofakind pretty much nailed it back in post #12 when he said to check the airbox for blockages...

Yea, i ONLY looked IN the air box like a nub...didnt really think to check the snorkel. Was all kinda new to me. 10 Points to Choneofakind!